1. Field of the Invention
The present invention generally relates to a droplet ejection device and a droplet ejection method, and more particularly to a droplet ejection device and a droplet ejection method for performing ejection of ink with high precision.
2. Description of the Related Art
Conventionally, a multi-nozzle ink-jet printing device having a printing head module in which a plurality of nozzles are arranged is proposed as an ink-jet printing device as a droplet ejection device which enables high-speed printing. This multi-nozzle ink-jet printing device uses a large number of nozzles, and it can perform printing at high speed with high density when recording information on a recording media, such as paper.
Generally, ink-jet printing devices can be classified into a continuation system and an on-demand system. The printing head module of the on-demand system is a droplet ejection unit in which a plurality of nozzles are arranged. For each nozzle, a drive voltage is applied to the piezoelectric element or heater element so that pressure is applied to the ink in the ink chamber having the nozzle as an opening, thereby ejecting an ink droplet from the nozzle.
The technology related to the printing head module of this type is already known. See Japanese Laid-Open Patent Application No. 2002-273890 and Japanese Laid-Open Patent Application No. 2002-120366. When compared with the continuation system, the on-demand system has a simple structure, and, in the printing head module of the on-demand system, several hundreds or thousands of nozzles can be arranged with high density.
Suppose a case in which the above-mentioned multi-nozzle ink-jet printing device is used and printing is performed to various recording media, such as recording boards or recording sheets, with which the permeability of ink differs. In is known that there is an optimum amount of ink spread per unit area for the recording media of different types, and as for the recording media of the same type there is also an optimum amount of applied ink per unit area according to the type of the recording medium.
When the ink spread is less than the optimum value, the optical density of a filled-in image falls or a thin line becomes blurred, and the quality of image deteriorates. On the other hand, when the ink spread (the amount of ink ejection) is more than the optimal value, the image runs or drying of ink delays. Or if the recording medium is paper, the ink goes through the back surface of the paper. The ink spread more than the optimum value means that an excessive amount of the ink large than the necessary amount is unnecessarily used.
Therefore, the optimum value of the ink spread must be kept by performing adjustment with high precision for every kind of the recording media.
In a case of a low-speed ink-jet printing device having a small number of nozzles, the ink spread can be adjusted with high precision by adjusting the drive voltage of the piezoelectric element or the number of minute ink droplets. However, in a case of a high-speed multi-nozzle ink-jet printing device, it is difficult to take a circuit configuration for performing highly precise fine adjustment. Also, with respect to the processing speed, it is difficult to keep up the processing with the fine adjustment.
In a case in which the adjustment of ink spread is performed with the number of droplets, if the diameter of droplet is large, a jitter will appear at the edge of the output image, and the quality of image will be degraded.